Fossil Fuckery Flashcards
Direct Preservation: Unaltered Remains
Preserved without any or very little change from original state, occurs in 3 ways: unaltered, desiccation, embedding
Unaltered
hard parts (bones, teeth, shells) remain unchanged because they are resilliant
Desiccation
Freezing or mummifcation
Embedding
in wax or amber (desiccation also occurs in this mode)
Direction Preservation: Altered Remains
- Most fossils are altered in some way. Changes may be chemical, physical, or both. Single fossil may have more than 1 or these forms:
1. Recrystallization
2. Replacement
3. Premineralization
4. Petrification
5. Carbonization
Recrystallization
Minerals of fossils change to a more stable form without change in composition. Involves increase in crystal size. In shells, makes them appear dull
Replacement
Minerals of a fossil are replaced by new minerals with different compositions. Usually replaced by silica or pyrite.
Permineralization
Pores (in bones usually) or empty body chambers are filled with a mineral, in wood as well
Petrification
Organic tissue of a fossil is replaced with new mineral
Carbonization
Volatiles (i.e water) are removed through heat and compaction leaving a thin carbon film
Indirect preservation: Impressions
Physical remains of buried organism dissolve, but the shape is still preserved in the fossil record
Molds
impression of remains like stamps of organisms = external mold. If interior of organism is filled with sediment/sedimentary minerals and shell dissolves away = internal mold
Casts
Exact replicas of remains. If an external mold later fills with sediment/mineral an exact replica/cast is made
Molds are negative
Inverse of the original shape
Casts are positive
Same as the original shape
Colonial Organisms
individuals living together in a single mass of interlocking, individual skeletons, recognized by presence of multiple openings which represent many individual homes
Solitary organisms
not structurally bound to any other organism
Steps in identifying fossil
- Colonial/solitary
2. Describe overall shape of fossil
Trace Fossils
- Objects or evidence of life activities fossilized in or on sediment layers
- Occur in marine and continental sedimentary rocks
Types of Trace Fossils
- Burrows and Borings
- Resting Traces
- Trackways, Trails and Footprints
- Coprolites and Gastroliths
Burrows and Borings
burrows in soft sediment or bore holes in solid rock/wood/shells, often tubular and horizontal for deposit feeding or dwelling
Resting traces
When an animal stops moving for a short while, producing a shallow impression or mold on the sediment surface, may record their shape or morphology
Trackways, Trails and Footprints
Evidence of animals travelling across soft sediment surfaces, preserved as molds on top of beds or casts on bottoms of overlying beds. Formed by organisms that are surface feeding or grazing.
Coprolites
fossil excrement
Gastroliths
Only identifiable if found in the gut area of a skeleton, rounded stomach stones used for grinding down food after its swallowed
Incomplete Fossil Record
- Likelihood of an organism becoming a fossil is determined by its: structure, composition and environment it lived/died in
- Because sediment is constantly transported to bodies of water, deposition occurs relatively continuously in these settings
- More likely to have marine and freshwater organisms preserved than terrestrial = more complete fossil record of marine realm
Fossils are generally better preserved in:
fine-grained sediment because fine grain sizes preserve small details
Fossil/Biotic Succession
Relative dating principle that states that fossils in sedimentary rock units occur in particular vertical order, reflecting changes due to evolution
Biostratigraphy/Biostratigraphic Correlation
Rock units in different locations can be correlated using the same principle and this method of showing correspondence of character and/or stratigraphic position between features or element in separate locations
Index groups
few select groups used for regional and intercontinental correlations, individual fossils used = index fossils
Index groups/fossils are abundant…
geographically widespread, and occur over restricted/short stratigraphic range = didn’t live for very long because evolved quickly or extinct
Biozone
A restricted sequence of rock strata that records a discrete interval of Earth history, used for determining the age of rocks from fossils, identified by presence of specific fossil or group of fossils